1. Field of the Invention
This invention relates to apparatus for producing a circumferential weld on a cylindrical vessel and more particularly to such apparatus that straddles the vessel.
2. State of the Prior Art
Apparatus presently utilized to produce such welds have been cantilever manipulators which consist of a motorized car which rides on a railway-type steel track. Extending vertically from the car is a mast that is capable of being rotated either electrically or mechanically. Extending horizontally from the mask is a boom, which is slidably disposed on the mast. The boom may be raised or lowered with respect to the mast and also extend inwardly or outwardly horizontally with respect to the mast. Welding equipment is mounted on one end of the horizontal boom and a welding operator's chair and control panel is mounted on the end to permit observation and control of the welding operation. The welding equipment, controls, and operator produce a concentrated load at the end of the boom that is cantilevered from the mast. This concentrated load at one end of the boom results in boom deflection, backlash in rotating and lifting mechanisms, and motion in the end of the boom due to movement of the operator. As cantilever manipulators age and the bearing surfaces and gears wear, the end of the boom becomes more unstable, thereby exhausting the probability of defects in the weld. The cantilever manipulators also require a large amount of floor space and operators feel insecure sitting on the end of the booms. Therefore, it is desirable to provide a welding manipulator which takes up less floor space, is more stable, and makes the operator feel secure.